The present invention relates to a temperature compensated crystal oscillator (TCXO) used for a communication system, a data processing system, and the like systems.
A TCXO which remains stable despite a change of the environmental temperature has been used to produce a reference or designated frequency in a mobile telephone system as reported in a paper entitled "800 MHz Band Land Mobile Telephone Radio System" by Terumochi Kamata et al., REVIEW OF THE ELECTRICAL COMMUNICATION LABORATORIES Volume 25, Numbers 11 to 12, December issue, 1977, pp. 1157 to 1171. Details of the construction and the operation of a TCXO is further discussed in a paper entitled "A microcircuit Temperature Compensated Crystal Oscillator (MCTCXO)" by L. Thoman, in the PROCEEDINGS OF THE 28th ANNUAL SYMPOSIUM ON FREQUENCY CONTROL 1974, pp. 214-220. Thoman's TCXO uses a temperature compensating circuit including three thermistors (RT.sub.1 to RT.sub.3) and a plurality of resistors (R.sub.A to R.sub.D), a piezoelectric crystal resonator (Y.sub.3) to determine an oscillating frequency, and varactors (CR.sub.2 and CR.sub.3) to change a load capacitor of the resonator. This makes the oscillator considerably complicated and costly to manufacture. The oscillator thus produced in therefore not suitable for the above-mentioned mobile telephone system, which is required to be of a simpler structure and a lower manufacturing cost.